Poly-n-vinyl-3-nitro carbazole photoconductive material

ABSTRACT

AN ORGANIC PHOTOCONDUCTIVE MATERIAL FOR USE IN ELECTROPHOTOGRAPHIC COPYING PAPER, SAID MATERIAL CONSISTING ESSENTIALLY OF POLY-N-VINYL-3-NITROSOCARBAZOLE WHICH IS QUITE EASILY SYNTHESIZED BY INTRODUCING A NITROSO RADICAL INTO POLY-N-VINYL CARBAZOLE, AND ALSO AN ELECTROPHOTOGRAPHIC COPYING PAPER PREPARED WITH A SUPPORT PAPER AND A LIGHTSENSITIVE LAYER WHICH IS FORMED WITH THE AFORESAID ORGANIC PHOTOCONDUCTIVE MATERIAL ON ONE SURFACE OF SAID SUPPORT PAPER.

United States Patent Ofice 3,595,548 Patented July 27, i971 3,595,648 POLY-N-VINYlL-Ct-NITRO CARBAZOlLE PHOTOCONDUCTIWE MATERIAL Kazuo 'lubuko, Tokyo, Japan, assignor to Kabushiki Kaisha Ricoh, Tokyo, Japan No Drawing. Filed Mar. 13, 1968, Ser. No. 712,590 Claims priority, application Japan, Mar. 23, 1967, 42/17,65l lint. Cl. G03g 5/06 US. Cl. 961.6 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION (a) Field of the invention The present invention is concerned with a novel organic photoconductive material for use in the formation of the light-sensitive layers of electrophotographic copying papers and it further relates to an electrophotographic copying paper which is formed with this novel photoconductive material as the principal component of the light-sensitive layer thereof.

(b) Description of the prior art As the organic photoconductive materials which have been commercially employed, those substances such as carbazole, anthraquinone, perylene and anthracene, polymers of these substances, and also a series of heterocyclic substances, are known. Most of these substances, however, have their spectral sensitivity only for those ultraviolet rays of a limited range of wavelengths, namely, 355 m more or less. For this reason, in case it was intended to use them in the formation of the light-sensitive layers of commercial electrophotographic copying papers, it was necessary to artificially expand their spectral sen sitivity over the range of visible rays by including a sensitizer such as a sensitizing dyestuff or an assistant sensitizer in the light-sensitive layers of those copying papers.

It has been impossible, however, to impart to such substances as carbazole, anthraquinone and perylene a high sensitivity to light to such an extent that become useful for the accomplishment of practical purposes even when a sensitizer was additionally introduced into such substances. Also, polymers of these substances required the use of a sensitizing dyestulf or like agents when it was intended to increase their light-sensitivity to such an extent that they would be sufficient for satisfying practical purposes. Furthermore, said series of heterocyclic substances per se lack a film-forming ability. For this reason, the formation of a light-sensitive layer by the use of a heterocyclic substance necessitated the employment of a binder such as synthetic resins. The inclusion of a binder in the lightsensitive layer which contains a heterocyclic substance, in turn, led to a reduction in the sensitivity to light of such layer, so that it was impossible in the past to obtain a copying paper which was capable of satisfying practical purposes. In addition, there was the inconvenience that the synthesis of heterocyclic substances required the employment of complicated manufacturing procedures.

SUMMARY OF THE INVENTION The present invention relates to an organic photoconductive material whose principal component consists of poly-N-vinyl-3-nitroso carbazole. This particular component possesses of various conveniences and advantages in that it can be manufactured easily by the adoption of a very simple synthesizing method, that it is of an excellent film-forming ability, and further that the lightsensitive layer formed on a copying paper and prepared with this component has a sufficiently high sensitivity to light even where the light-sensitive layer which is provided thereon contains no sensitizing agent such as a sensitizing dyestutf or an assistant sensitizer, so that the light-sensitive layer which is formed by the use of only this particular component will provide a good copying paper which is sufficiently satisfactory for the attainment of practical purposes.

It is, therefore, the primary object of the present invention to provide an organic photoconductive material as has been described above which has a suflicient sensitivity to light without the joint use of a sensitizer and/ or an assistant sensitizer and which adheres firmly to a support paper to thereby permit a light-sensitive layer to be formed thereon without requiring the employment of a binder.

Another object of the present invention is to provide a solution which is intended for use in the formation of a light-sensitive layer for copying papers and which is prepared by the use of the aforesaid organic photoconductive substance of the present invention.

Still another object of the present invention is to provide an electrophotographic copying paper which is manufactured by the use of the aforesaid organic photoconductive material.

It is to be noted, however, that the light-sensitive layer which is prepared by the combined use of the organic photoconductive material of the present invention and a sensitizer will exhibit a further improved sensitivity to light.

For example, the additional use of a sensitizer of a given amount will increase the light-sensitivity of the poly-N-vinyl-3-nitroso carbazole of the present invention to a degree which is by far greater than that which is attained when the same amount of sensitizer is introduced to such substances as poly-N-vinyl carbazole and poly-N-vinyl-nitro carbazole.

This will be explained by the fact that, owing to this nitroso radical not being a powerful electron-attracting substituted radical as is the nitro radical, the sensitizing dyestutf and the assistant sensitizer can act effectively on the nitroso radical and also that the nitroso radical will readily form a complex in joint cooperation with the halogenated metal or like materials of the assistant sensitizer employed.

Description will next be directed to the examples of the manner in which the poly-N-vinyl-3-nitroso carbazole is synthesized.

SYNTHESIS EXAMPLE 1 First, 5 gr. of poly-N-vinyl carhazole was dissolved in gr. of monochloro benzene. To this solution was added another solution which was prepared by dissolving 2.5 gr. of hydrochloric acid (12 N) in 5 gr. of methanol. While stirring the resulting mixed solution thoroughly and holding it at about 8 C., a liquid which was a mixture of 3 gr. of sodium nitrite and 5 gr. of methanol was gradually introduced, in drops, into said mixed solution, consuming 2 hours till the completion of the introduction of said liquid. The reaction was completed at the end of about 5 hours. As a result, a product bearing a yellow green color was obtained. This product was then treated with either water or alcohol to deposit crystals of coarse product. After washing this product thoroughly to remove the adhering sodiumnitrite and acids, the resulting product was dried, for 4 hours, in a constant temperature vessel which was held at a temperature ranging from 80 C. to 100 C. As a result, the desired product was obtained.

SYNTHESIS EXAMPLE 2 gr. of poly-N-vinyl carbazole was dissolved in 95 gr. of monochloro benzene. Into this solution was added 0.5 gr. of hydrochloric acid (12 N) or glacial acetic acid. The resulting mixed solution was cooled to 5 C. and was stirred thoroughly. Aside from this, a total of 250 gr. of hydrochloric acid of 6 N was gradually added in drops, by the use of Kipps apparatus, to 20 gr. of sodium nitrite for reaction therewith to thereby generate N0 gas. This N0 gas was introduced into the resulting mixed liquid of poly-N-vinyl carbazole and acids, while exercising caution so that the N0 gas would not be converted to N0 gas. In this instance, the reaction would proceed without the addition of acids to poly-N-vinyl carbazole. It was noted to be desirable, however, to introduce the gas in a large amount at the initial stage of the reaction and to reduce the supply gradually thereafter. The reaction was completed substantially at the end of 3 hours. The reaction product obtained bore a yellow green color. This product could, of course, be used directly as the desired product of the present invention. It was noted to be more desirable, however, if this reaction product was washed with either water or methanol and was thereafter dried for 4 hours in a constant temperature vessel which was held at 100 C. and was then pulverized into powder as the final product.

Poly-N-vinyl-3-nitroso carbazole obtained from a synthesizing procedure as has been described in the foregoing two examples is dissolved in a solvent which may be monochloro benzene, dimethyl formamide, methylene chloride and methyl cellosolve. The resulting solution is applied onto one surface of a support paper which has been already given an electroconducting treatment, and the resulting support is dried. As a result, an electrophotographic copying paper is obtained. In the event it is desired to obtain a copying paper having a higher sensi tivity to light, it is only necessary to form a light-sensitive layer by the use of a solution which is prepared by admixing a sensitizing dyestufl and/or an assistant sensitizer in the aforesaid organic photoconductive material which is the product obtained according to the present invention.

The organic photoconductive material of the present invention possesses a spectral sensitivity not only in the range of visible rays of wavelengths from 380 my. to 780 m but also in ultraviolet rays which have wavelengths smaller than 380 mp. As such, the organic photoconductive material of the present invention possesses both of the two desirable properties, i.e. the so-called optical sensitization effect and the so-called chemical sensitization eifect which means the intensity of the sensitivity to light of a given wavelength. In the event that an electric charge is impressed, by corona discharge, onto the copying paper formed with a support paper (which may be made with paper, a plastic film, a sheet-form material or an acetate film, each having its reverse surface that has been given an electroconducting treatment, or which may be made with an electroconductive metal sheet) having its upper surface provided with a light-sensitive layer which contains the aforesaid organic photoconductive material of the present invention, the copying paper is charged up to a sufficiently satisfactory potential which, for example, is in the range of from 250 volts to 500 volts, and thus, the copying paper is imparted with an electrostatic sensitivity to light. In case this copying paper is exposed to light coming from a lamp such as a tungsten lamp which is adapted to emit visible rays chiefly, the

potential of the light-sensitive layer of this copying paper drops quickly owing to its intensive spectral sensitivity as has been referred to above. Accordingly, by impressing an electric charge onto the light-sensitive layer of this copying paper by the use of a commercially available electrophotographic copying apparatus and exposing the light-sensitive layer to light through an overlaid original which carries an image to be copied, the portions of the light-sensitive layer which are located immediately beneath the image of the original are maintained high in potential. Whereas, the potential of those portions of the light-sensitive layer which are located closely under and adjacent to the non-image areas of the original drops rapidly. In this way, there is rapidly formed an electrostatic latent image in the light-sensitive layer. Thus, the adoption of the electrophotographic copying paper which is obtained according to the present invention greatly improves the velocity of the copying operation as compared with the velocity With which copies are taken by the use of the conventional copying papers which are formed with the organic photoconductive materials of the prior art. Besides, when the exposed copying paper of the present invention is developed according to the wet development process or the dry development process, there is invariably formed a very clear and well-contrasted copied image on the face of the copying paper, because of the very distinct difference in the level of potential between the electrostatic latent image portion and the non-image portion of the copying paper due to the reasons as have been stated already.

As the sensitizing dyestuffs which can be used in combination with the organic photoconductive material of the present invention, those substances such as Methyl Violet (0.1. No. 42535), Crystal Violet (C.I. No. 42555), Methylene Blue FZ (C.'I. No. 52015), Methylene Blue BH (C.I. No. 52015), Victoria Pure Blue B (CJI. 44045), Brilliant Green (C.I. No. 42000) and Malachite Green (0.1. No. 42000), are desirable.

As the assistant sensitizers which can be used in the present invention, those acids such as acetic acid, monochloro acetic acid, dichloro acetic acid, trichloro acetic acid, picric acid, phthalic acid, their acid anhydrides; metal halides such as zinc chloride, aluminum chloride, ferric chloride and zinc nitrate; quinones such as benzoquinone; aldehydes and ketones, are desirable. By the joint use of such a substance as those enumerated above, it is possible to obtain a copying paper having a further increased sensitivity to light. Also, the amount of the sensitizing dyestuff and/ or the assistant sensitizer as tho e enumerated above which are blended with the aforesaid organic photoconductive material of the present invention, desirably, is in the range of from 0.1 to 5.0 parts by weight per parts by weight of the organic photoconductive material. Furthermore, in view of the fact that the organic photoconductive material of the present invention is of a highly increased light-transmitting property, it is to be noted that the electrophotographic copying paper whose light-sensitive layer is formed with this organic photoconductive material on a transparent support can be effectively used as the secondary original for the conventional diazotype photographic copying papers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 0.75 gr. of poly-N-vinyl-3-nitroso carbazole which was obtained in the Synthesis Example 1 was dissolved in 14 gr. of monochloro benzene. The resulting solution was applied onto the upper surface of an art paper whose reverse face had been given an electro-conducting treatment, in such a way that the layer of the solution was of a thickness of 3 After forming a light-sensitive layer in this way on said support paper, the latter was dried at 120 C. for 2 minutes to regulate the moisture content to 4.5%. As a result, an electrophotographic copying paper was obtained.

The copying paper obtained in the manner described above was then subjected to corona discharge to impress the light-sensitive layer thereof with negative charge. Thereafter, the copying paper was exposed, through an original which was laid thereon, to light coming from a tungsten lamp of 800 Lux which was located at a distance of 35 cm. from said copying paper. The exposed copying paper was then developed according to the wet development process. As a result, a very wellcontrasted copied image was obtained.

Example 2 0.75 gr. of poly-N-vinyl-3-nitroso carbazole obtained in the aforesaid Synthesis Example 2 was dissolved in 14 gr. of methyl cellosolve. Then, 0.02 gr. of zinc nitrate was added to this solution to be dissolved therein. Using an acetate film which had been given an electroconducting treatment, the resulting mixed solution was applied onto the upper face up to a thickness of 4 followed by drying the same at 120 C. for 2 minutes. As a result, an electrophotographic copying sheet was obtained. The copying sheet thus obtained was then subjected to a copying process in the manner same as that described in Example 1, with the result that a very well-contrasted copied image Was obtained. This copy was suitable for use as the secondary original for diazotype photographic copying papers.

Example 3 0.75 gr. of poly-N-vinyl-3-nitroso carbazole obtained according to the Synthesis Example 2 was dissolved in 14 gr. of monochloro benzene. To this solution was added further 0.225 cc. of Methylene Blue FZ (a solution of 1% methanol) and also 0.1 cc. of picric acid. After stirring the mixture thoroughly, the resulting solution was applied onto one face of a tracing paper sheet (60 gr./ m?) which had undergone an electroconducting treatment in such a way that the solution was provided thereon to a thickness of 4 1.. After drying the resulting copying sheet at 120 C. for 2 minutes and regulating the moisture content to 4.3%, an electrophotographic copying sheet was obtained. It was noted that the velocity of the light decay (meaning the dropping velocity of the potential of the charged light-sensitive layer) of this copying sheet when it was exposed to light was times greater than that observed on the copying sheet where the lightsensitive layer was formed with only poly N-vinyl-3- nitroso carbazole. It was noted also that the velocity of the light decay of the copying sheet obtained in this example was 1.2 times greater as compared with that observed on the copying sheet where the light-sensitive layer was formed with poly-N-vinyl carbazole and sensitized in the same manner as that described in this example. It was noted further that the velocity of the light decay of the copying sheet of this example was 1.4 times greater than that observed on the copying sheet whose light-sensitive layer was formed with poly-N-vinyl-1,3- nitro carbazole.

What is claimed is:

1. An organic photoconductive material for use in electrophotographic copying'papers, said material consisting essentially of photoconductive poly N vinyl-3- nitroso carbazole.

2. An organic photoconductive material for use in electrophotographic copying papers, said material being a solution wherein photoconductive poly N vinyl 3- nitroso carbazole is dissolved in an organic solvent selected from the group consisting of monochloro benzene, dimethyl formamide, methylene chloride and methyl cellosolve.

3. An electrophotographic copying sheet comprising a support and a light-sensitive layer formed on one surface of said support and containing a photoconductive material, said light-sensitive layer being formed with an organic photoconductive material consisting essentially of poly-N-vinyl-3-nitroso carbazole.

4. An organic photoconductive material according to claim 1, wherein said material contains blended therewith a sensitizer in an amount in the range of from 0.1 to 5.0 parts by weight of the sensitizer per parts by Weight of said poly-N-vinyl-3-nitroso carbazole, said sensitizer being at least one member selected from the group consisting of Methyl Violet (Cl. No. 42535), Crystal Violet (Cl. No. 42555), Methylene Blue FZ (Cl. No 52015), Methylene Blue BH (C.I. No. 52015 Victoria pure Blue B (C.I. No. 44045), Brilliant Green (C.I. No. 42000), Malachite Green (Cl. No. 42000), acetic acid, monochloro acetic acid, dichloro acetic acid, trichloro acetic acid, picric acid, phthalic acid, anhydrides of said acids, zinc chloride, aluminum chloride, ferric chloride, zinc nitrate, quinones, aldehydes and ketones.

5. An organic photoconductive material according to claim 2, wherein said solution contains mixed therewith a sensitizer in an amount in the range of from 0.1 to 5.0 parts by weight of the sensitizer per 100 parts by weight of said poly-N-vinyl-3-nitroso carbazole, said sensitizer being at least one member selected from the group consisting of Methyl Violet (C.I. No. 42535), Crystal Violet (C1. No. 42555), Methylene Blue FZ (C.I. No. 52015), Methylene Blue BH (OJ. No. 52015), Victoria pure Blue B (01. No. 44045), Brilliant Green (C.I. No. 42000), Malachite Green (C.I. No. 42000), acetic acid, monochloro acetic acid, dichloro acetic acid, trichloro acetic acid, picric acid, pthalic acid, anhydrides of said acids, zinc chloride, aluminum chloride, ferric chloride, zinc nitrate, quinones, aldehydes and ketones.

6. An electrophotographic copying sheet according to claim 5, wherein said light-sensitive layer contains blended therewith a sensitizer in an amount in the range of from 0.1 to 5.0 parts by weight of the sensitizer per 100 parts by weight of said poly-N-vinyl-3-nitroso carbozole, said sensitizer being at least one member selected from the group consisting of Methyl Violet (C.I. No. 42535), Crystal Violet (C.I. No. 42555 Methylene Blue FZ (C.I. No. 52015), Methylene Blue BH (C.I. No. 52015), Victoria pure Blue B (CI. No. 44045 Brilliant Green (C.I. No. 42000), Malachite Green (C.I. No. 42000), acetic acid, monochloro acetic acid, dichloro acetic acid, trichloro acetic acid, picric acid, phthalic acid, anhydrides of said acids, zinc chloride, aluminum chloride, ferric chloride, zinc nitrate, quinones, aldehydes and ketones.

References Cited UNITED STATES PATENTS 3,037,861 6/1962 Hoegl et al. 96-1 3,130,060 4/1964 Cassiers et. al. 96-1 3,312,673 4/1967 Hewett 260-803 3,421,891 1/1969 Inami et a1 961.6 3,464,819 9/1969 Inami et al. 961.5

OTHER REFERENCES Chemical Abstracts, vol. 68, 1968, col. 12,858c.

GEORGE F. LESMES, Primary Examiner I. C. COOPER III, Assistant Examiner US. Cl. X.R. 

